A cement admixture is widely used for a cement composition such as cement paste, mortar, or concrete.
The use of the cement admixture can increase the fluidity of the cement composition, and can reduce water in the cement composition. The water reduction leads to improvements in strength, durability, and the like of a cured product.
In recent years, a cement admixture including a polycarboxylic acid-based copolymer as a main component has been proposed as the cement admixture. A cement admixture (polycarboxylic acid-based cement admixture) including a polycarboxylic acid-based copolymer as a main component can exhibit high water-reducing performance.
As for the polycarboxylic acid-based copolymer capable of exhibiting high water-reducing performance in the case of being used for the cement admixture, there is known a polycarboxylic acid-based copolymer including a structural unit derived from an unsaturated polyalkylene glycol ether-based monomer and a structural unit derived from an unsaturated carboxylic acid-based monomer (see Patent Literatures 1 to 9).
However, there is a problem in that the unsaturated polyalkylene glycol ether-based monomer has low copolymerization property as compared to a corresponding ester-based monomer, for example. Therefore, in the production of the polycarboxylic acid-based copolymer including a structural unit derived from an unsaturated polyalkylene glycol ether-based monomer and a structural unit derived from an unsaturated carboxylic acid-based monomer, the following problems may arise, for example. That is, when it is intended to obtain a polycarboxylic acid-based copolymer having a desired copolymerization ratio, such copolymer cannot be obtained. Even when such copolymer is obtained, the polymer purity decreases to deteriorate polymer quality, and the production cost increases because polymerization must be performed under a low concentration condition. Further, when the polycarboxylic acid-based copolymer including a structural unit derived from an unsaturated polyalkylene glycol ether-based monomer and a structural unit derived from an unsaturated carboxylic acid-based monomer is used for a cement admixture, the performance of the cement admixture cannot be sufficiently expressed owing to the above-mentioned low copolymerization property.
Further, in the hitherto reported copolymerization methods for the production of the polycarboxylic acid-based copolymer including a structural unit derived from an unsaturated polyalkylene glycol ether-based monomer and a structural unit derived from an unsaturated carboxylic acid-based monomer, sufficient copolymerization property cannot be easily expressed for the unsaturated polyalkylene glycol ether-based monomer. Accordingly, in the production of the polycarboxylic acid-based copolymer including a structural unit derived from an unsaturated polyalkylene glycol ether-based monomer and a structural unit derived from an unsaturated carboxylic acid-based monomer, the development of a technology that allows for easy expression of sufficient copolymerization property for the unsaturated polyalkylene glycol ether-based monomer can reduce the production cost of the copolymer and can produce a polycarboxylic acid-based copolymer with which an unprecedentedly high-performance cement admixture can be provided.